1. Field of Use
This invention relates generally to a fastener assembly commonly known as an "expansion rivet" or a "blind rivet" and comprising a hollow plastic expandable rivet and a plastic pin axially movable in the rivet to cause rivet expansion.
2. Description of the Prior Art
Fasteners of the aforesaid general character are known and in use and U.S. Pat. No. 4,222,304 for "BLIND RIVET" illustrates the state of the art. That patent discloses a blind rivet which is injection molded from plastic material. It comprises a female member molded about a male member. The female member is comprised of a flexible tubular wall and a flange about the upper end thereof, the wall defining a stepped portion in the axial bore thereof at the upper end and a plurality of elongate perforations about the wall. The male member is comprised of a shank in the axial bore and axially movable in relation to the tubular wall, an enlarged head at one end in intimate contact and engagement with the lower end of the female member, and a head portion at the other end and protruding from the upper end of the female member. The head portion is shaped to be gripped by a tool for pulling the shank axially through the bore and the shank has a series of peripheral claws each forming a shoulder facing the lower end so that, upon pulling, the perforated flexible tubular wall collapses and expands radially and successive claws snap their respective shoulders into engagement with the shoulder of the stepped portion, the engagement of the shoulders maintaining the tubular wall of the female member radially expanded and locking the male member against axial movement towards the lower end of the female member.
In the above-described prior art fastener the male and female members are molded together, one about the other, during manufacture in a so-called "two shot" molding process and are not separable, even though separability of the fastener components is sometimes desirable during fastener installation if clearance is a problem. Furthermore, since interengaging serrations are necessarily formed on the prior art male and female members during manufacture, considerable force is required initially to effect axial movement of the pin in the rivet before expansion of the rivet walls occurs. In addition, the prior art pin is so constructed that the portion thereof which protrudes from the rivet after fastener installation must be cut off in a discrete step by means of a cutting tool. In particular, since the prior art rivet and pin are molded together by the "two-shot" molding process, it is not practical to mold a break-away indentation or groove in the pin because this groove would fill with plastic material from formation of the rivet therearound.